The magnetic device described in my U.S. Pat. No. 3,820,090 issued June 24, 1974 is a ferro-magnetic wire having core and shell protions with divergent magnetic properties. As taught in my U.S. Pat. No. 3,892,118 issued July 1, 1975 this device is made by applying a cycling torsional strain to the wire so as to circumferentially strain the wire. The wire is torsionally strained in alternate clockwise and counterclockwise directions while maintaining axial tension on the wire. The result is a wire which, it is believed, because it has a relatively harder magnetic shell and a relatively softer magnetic core, has the property that, once magnetized, the magnetically harder shell can capture the magnetically softer core.
When the wire is magnetized and then subjected to an increasing external magnetic field that is parallel to the axis of the wire, a threshold is reached where the external field suddenly captures the core thus rapidly reversing the magnetization of the core. A pick-up coil around the wire will produce a pulse in response to the rapid change in the direction of flux in the core. The reversal of core magnetization occurs in response to the external magnetic field intensity exceeding a threshold and is substantially rate insensitive. That is, the magnitude of the output pulse is only slightly dependent on the rate-of-change of applied field as it passes through the threshold value. This is to be contrasted with more conventional pulse generating circuits based on soft magnetic materials whose hysteresis loops are continuous. The output-pulse amplitude (and the inverse of the pulse width) of this latter class of devices is essentially proportional to the time-rate-of-change of the field as it passes through the coercive force.
Similarly, there is a reverse switch in core magnetization and a reverse pulse generated in the pick-up coil as the external magnetic field decreases past a second threshold. Again, the pulse output is substantially independent of the rate at which the magnetic field decreases; all that is required is that the switching threshold is passed.
The magnitude of the output pulse is of critical importance in determining the value of the wire and in determining the scope of applications to which the wire can be commercially put. The larger the pulse, the less will be required in the way of electronic circuitry associated with the pick-up coil to distinguish the pulse from background noise. The larger the pulse amplitude, the more repeatable will be any output condition that is to be initiated or recorded by the incidence of the pulse.
Accordingly, it is a major purpose of this invention to provide an improved switching device of the type described in the above patents that responds to a threshold external magnetic field to produce a pulse having improved signal to noise ratio and a larger peak amplitude.
It is a related and further important purpose of this invention to provide such an improved wire as will provide the kind of switching response to the threshold magnetic field that will produce a uniform and repeatable output pulse from a pickup coil.
The above mentioned patents describe a magnetic device having two magnetic states, a reverse state in which core and shell have opposite directions of magnetization and a confluent state in which core and shell have the same direction of magnetization.
In brief, the wire disclosed in U.S. Pat. No. 3,820,090 is made from a commercially available wire, having in one embodiment a 0.25 mm diameter and an alloy composition that is 48 percent iron and 52 percent nickel.
In brief, the method of manufacturing disclosed in U.S. Pat. No. 3,892,118 for the wire switching device comprises the use of a fine grain nickel-iron alloy having for example, a 0.25 mm diameter. A one meter length of this wire is elongated four centimeters. The elongated wire is held under tension between two chucks and cycled counterclockwise and clockwise at a rate of 0.4 turns per centimeter of wire. Thus for the one meter length of wire, the chucks rotate 40 complete revolutions in one direction and then 40 complete revolutions in the other direction. This clockwise and counterclockwise rotation is repeated ten to fifteen times. The chucks are supported in a machine which maintains a constant tension of 450 grams as the rotation occurs. After this processing, the tension is removed and the one meter length of wire is cut into whatever lengths are desired (usually about one to three cm each) for use in the various switching and pulse generating applications which have been developed for this wire.
Some variation in tension, number of turns per meter and number of cycles of clockwise and counterclockwise rotation are desirable as a function of wire diameter, wire chemistry and application in which the wire is to be used.